1. Field of the Invention
The present invention relates to a route guidance apparatus, and in particular, to route guidance apparatus employing a Universal Traffic Management System (UTMS), such as via road beacons and car telephones.
2. Description of the Related Art
A UTMS has been developed in which a vehicle's destination data is transmitted, such as from the vehicle to a road beacon, and a control center, such as one connected to the road beacon, a recommended route to the destination taking into account traffic conditions is calculated, and route information to the vehicle via the road beacon is returned. Various types of traffic information (such as traffic congestion information and accident information) are gathered at the control center so that a more suitable route to the destination can be presented to the vehicle compared to what can be obtained by simply considering only map data.
However, the vehicle's destination does not always fall within the service area of the UTMS. A problem in such a case is that, even if destination data is transmitted from the vehicle, the control center cannot present a route to the vehicle using UTMS.
Japanese Laid-Open Publication No. Hei 7-234995, for example, therefore proposes a technique for transmitting to a road beacon coordinates corresponding to the farthest link from the present position on a route calculated at the vehicle and within the area in which routes can be provided by the control center as a temporary destination.
According to this technique, a recommended route can be reliably obtained from the control center. However, since a temporary destination to be transmitted to the control center is not determined until route searching completes at the vehicle, a problem is that the UTMS service cannot be received even though a user may have set the destination and the vehicle passes a road beacon. Of course, with road beacons installed to a certain extent in close proximity to each other, any time loss can be practically eliminated even after a road beacon is passed, provided the route search processing completes before the next road beacon is passed and a temporary destination can be transmitted to that next road beacon. However, since the intervals between road beacons are large, especially outside the major cities, a problem is that a considerable amount of time is required from the setting of the destination until the obtaining of a suitable recommended route from the control center.